Effects of substituent branching and chirality on the physical properties of ionic liquids based on cationic ruthenium sandwich complexes

An appropriate understanding of how substituents affect the physical properties of ionic liquids is important for the molecular design of ionic liquids. Toward this end, we investigated how the branching and chirality of substituents affect the physical properties of organometallic ionic liquids. We synthesized a series of ionic liquids bearing a branched or linear alkoxy group with the same number of carbons: [Ru(C5H5)(η(6)-C6H5OR)]X (rac-[1]X: R = -CH(C2H5)(C6H13), [2]X: R = -CH(C4H9)2, [3]X: R = -C9H19), where X = PF6(-), (SO2F)2N(-), and (SO2CF3)2N(-). rac-[1]X are racemic salts. Salts with less symmetrical substituents tend to maintain the liquid state due to suppression of crystallization; crystallization is completely suppressed in most of the rac-[1]X salts and in some of the [2]X salts, whereas not in [3]X salts. The glass-transition temperatures and viscosities of the salts with branched substituents are greater than those with linear substituents. Chiral resolution of rac-[1][PF6] was performed by chiral chromatography. The melting point of rac-[1][PF6] is much lower than that of the enantiopure salt (chiral-[1][PF6]), which we ascribe to the formation of a conglomerate in the solid state. X-ray structure analysis revealed that the solid salts form layered structures.

Computational insights into the molecular interaction and ion-pair structures of a novel zinc-functionalized ionic liquid, [Emim][Zn(TFSI)₃]

The ion pair structures of a novel CO2 capture material in the form of a metal chelate anion-containing room temperature ionic liquid (IL), 1-ethyl-3-methylimidazolium tri[bis(trifluoromethylsulfonyl)imide]zincate(II), [Emim][Zn(TFSI)3], were elucidated by correlating the infrared spectra generated using density functional theory (DFT) calculations with the experimental spectrum derived from a room temperature infrared spectroscopic measurement. A free volume energy minimization algorithm revealed stable structures where the zinc ion forms an octahedral, homoleptic complex with the ligand bis(trifluoromethylsulfonyl)imide through coordination with the oxygen of the sulfone group, with 1-ethyl-3-methylimidazolium acting as the counterion. The method of analysis was built around 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [Emim][TFSI], involving direct comparison with published data, and extended to the more complex [Emim][Zn(TFSI)3] system. The DFT calculations reproduced the vibrational spectra of [Emim][Zn(TFSI)3] and [Emim][TFSI] using their optimized geometries, with correlation slopes of 0.9996 and 1.0022, respectively. Comparison of the vibrational modes of [Emim][TFSI] and [Emim][Zn(TFSI)3] provided insights into the ion pair structure of, and molecular interactions in the ILs analyzed.

Identification of single nucleotides in MoS2 nanopores

The size of the sensing region in solid-state nanopores is determined by the size of the pore and the thickness of the pore membrane, so ultrathin membranes such as graphene and single-layer molybdenum disulphide could potentially offer the necessary spatial resolution for nanopore DNA sequencing. However, the fast translocation speeds (3,000-50,000 nt ms(-1)) of DNA molecules moving across such membranes limit their usability. Here, we show that a viscosity gradient system based on room-temperature ionic liquids can be used to control the dynamics of DNA translocation through MoS2 nanopores. The approach can be used to statistically detect all four types of nucleotide, which are identified according to current signatures recorded during their transient residence in the narrow orifice of the atomically thin MoS2 nanopore. Our technique, which exploits the high viscosity of room-temperature ionic liquids, provides optimal single nucleotide translocation speeds for DNA sequencing, while maintaining a signal-to-noise ratio higher than 10.

Colorless organometallic ionic liquids from cationic ruthenium sandwich complexes: thermal properties, liquid properties, and crystal structures of [Ru(η(5)-C5H5)(η(6)-C6H5R)][X] (X = N(SO2CF3)2, N(SO2F)2, PF6)

A series of ionic liquids containing cationic ruthenium complexes ([Ru(C5H5)(C6H5R)](+)) were prepared, and their thermal properties were investigated (R = C4H9 (1a), C8H17 (1b), OCH2OCH3 (2a), O(CH2CH2O)2CH3 (2b), O(CH2)3CN (3a), O(CH2)6CN (3b), CO(CH2)2CH3 (4a), CO(CH2)6CH3 (4b)). Bis(trifluoromethanesulfonyl)amide (TFSA) and bis(fluorosulfonyl)amide (FSA) were used as counter anions. These ionic liquids were colorless and stable toward air and light. These salts exhibited glass transitions upon cooling from the melt (Tg = −82 °C to −55 °C), and the glass transition temperatures of the salts increased as the polarity of the substituents increased (alkyl < ether < cyano < carbonyl). The decomposition temperatures decreased in the order of alkyl > cyano > carbonyl > ether. The viscosities, solvent polarities, and refractive indices of the salts of 1a and 2a were also evaluated. Hexafluorophosphate (PF6) salts were also prepared, which were solids with high melting points (Tm = 65–127 °C). X-ray crystal structure analyses of these salts revealed the importance of intermolecular contacts involving the ring hydrogens. The PF6 salt of 2a exhibited an order–disorder phase transition.

Effects of Te(IV) Oxo-Anion Incorporation into Thorium Molybdates and Tungstates

The exploration of phase formation in the Th-Mo/W-Te systems has resulted in four mixed oxo-anion compounds from high-temperature solid-state reactions: ThWTe2O9, Th(WO4)(TeO3), ThMoTe2O9, and Th2(MoO4)(TeO3)3. All four compounds contain edge-sharing thorium polyhedra linked by MoO4/WO6 and different tellurium oxo-groups to form three-dimensional frameworks. In ThWTe2O9, each helical Th based chain is connected by four tungstotellurite clusters resulting in a building fragment which has a cross-section of four-leafed clovers. The structure of Th(WO4)(TeO3) exhibits a multilayer-sandwich framework composed of thorium tellurite layers with tungsten chains in between. In the case of the molybdate family, ThMoTe2O9 and Th2(MoO4)(TeO3)3 are built from puckered Th-Te sheets which are further interconnected by MoO4 tetrahedral linkers. The DSC-TG technique was performed to gain insight into the thermal behavior of the synthesized compounds. Raman spectra of as-prepared phases were obtained and analyzed for signature peaks.

Long-lived luminescent soft materials of hexanitratosamarate(III) complexes with orange visible emission

Sm(III)-based ionic liquids incorporating hexanitratosamarate(III) anions were obtained and fully characterized as novel Sm(III)-containing organic complexes. The structure of the ionic liquids was determined by single-crystal X-ray diffraction (1: monoclinic system C2/c space group with cell parameters: a = 19.5624(4) Å, b = 10.11895(18) Å, c = 33.2256(6) Å, β = 101.2912(18)°, Z = 8). The central Sm(III) ion is 12-coordinated by six bidentate nitrate ligands with twelve oxygen donors to form a [Sm(NO3)6](3-) anion. The low melting point, high thermostability and wide liquid range of these ionic liquids were determined in detail. All the complexes 1-5 display orange luminescence, rather than red luminescence as in most Sm(III)-containing organic complexes. Three characteristic monochromatic bands and an intense emission, derived from (4)G5/2→(6)HJ (J = 5/2, 7/2, and 9/2) intraconfigurational f-f transitions, were revealed. All these complexes exhibit long luminescence lifetimes.

Secondary amine based ionic liquid: an efficient catalyst for solvent free one pot synthesis of xanthenes and benzoxanthenes

Amine based ionic liquid was reported as an efficient and easily recyclable catalyst for the solvent free environmental benign synthesis of xanthene and benzoxanthene derivatives within 10–30 minutes.

Updating biomass into functional carbon material in ionothermal manner

The development of meaningful ways to transfer biomass into useful materials, more efficient energy carriers, and/or carbon storage deposits is a profound challenge of our days. Herein, an ionothermal carbonization (ITC) method, via treating natural resources (glucose, cellulose, and sugar cane bagesse) in nonmetal ionic liquids (ILs) at ∼200 °C, is established for the fabrication of porous heteroatom-doped carbon materials with high yield. Commercial ILs with bulky bis(trifluoromethylsulfonyl)imide anion or cross-linkable nitrile group were found to be efficient and recyclable templates for porosity control, leading to exciting nanoarchitectures with promising performance in oxygen reduction reaction. The optimized ILs (12 mL) can dissolve and directly convert up to 15 g of glucose into porous carbon materials (SBET: 272 m(2)/g) one time. This ITC method relies on the synergistic use of structure-directing effect, good biomass solubility, and excellent thermal stability of ILs, and provides a sustainable strategy for exploiting biomass.

Novel luminescent soft materials of terpyridine-containing ionic liquids and europium(III)

Herein, we describe novel luminescent soft materials via reaction of Eu(3+)-coordinated carboxyl functionalized ionic liquids with terpyridine-functionalized imidazolium salts that are built from an imidazolium ring substituted on one side with a terpyridine derivative and, on the opposite side, a paraffin chain of various lengths. The obtained materials are either pastelike substances or viscous fluids, depending on the anions of the carboxyl functionalized ionic liquids. The soft luminescent materials were investigated by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), thermogravimetry (TG), and luminescence spectroscopy. The soft materials show bright red emission irradiated with UV light, because of the energy transfer from terpyridine-functionalized imidazolium salts to the Eu(3+) ions. The absolute quantum yields of the materials were determined and the energy transfer efficiency was estimated according to the reported method.

Organometallic ionic liquids from alkyloctamethylferrocenium cations: thermal properties, crystal structures, and magnetic properties

Alkyloctamethylferrocenium salts with the Tf2N anion ([Fe(C5Me4C(n)H(2n+1))(C5Me4H)][Tf2N]; Tf2N = bis(trifluoromethanesulfonyl)amide) were prepared, and their ionic liquid properties, thermal properties, crystal structures, and magnetic properties were investigated. The melting points of the Tf2N salts were near room temperature, and decreased with increasing alkyl chain length up to n = 8 and then increased. The salts with PF6 and NO3 anions were also prepared. The melting points of the PF6 salts were higher than 100 °C. Most of these salts exhibited phase transitions in the solid state. The sum of the entropies of the melting and solid phase transitions was nearly independent of the alkyl chain length for salts with short alkyl chains, whereas those for salts with longer alkyl chains (n≥ 10 for Tf2N salts, n≥ 6 for PF6 salts) increased with increasing alkyl chain length. Crystal structure determinations revealed that the short chain salts form simple alternately packed structures of cations and anions in the solid state, and that the long chain salts form lamellar structures, in which the alkyl chains are aligned parallel between the layers. The effects of magnetic fields on the crystallization of the paramagnetic ionic liquids were investigated, and revealed that the Tf2N salts with n = 4 exhibited magnetic orientation when solidified under magnetic fields. The magnetic orientation was shown to be a bulk phenomenon, and the importance of the magnetic anisotropy of the crystal structure was suggested in comparison with the response of other Tf2N salts.